In the past, various different methods have been employed to fabricate electrical contacts and to provide contact surfaces on such electrical contacts having various different configurations.
One of the aforementioned past fabricating methods utilized a preformed electrical contact of the composite type, and such electrical contact included a generally circular base formed of copper or a copper alloy and having a pair of opposite faces, a stem integral with the base and extending therefrom, and a layer of a noble or precious metal overlaying the other of the opposite faces in bonded relation therewith with the precious metal layer defining a predetermined or preform contact surface on the electrical contact. The base, stem and contact surface of the electrical contact each extended about a centerline axis of the electrical contact.
In the past fabricating method of the aforementioned electrical contact, an ultrasonically actuated die was engaged with the contact surface of such electrical contact, and a cavity in such die was located generally about the centerline axis of such electrical contact Of course, in response to the ultrasonic actuation of the die, the die was moved or jiggled with a random reciprocal or back and forth movement against the precious metal of the contact surface, and some of the precious metal was randomly scraped or scrubbed from the contact surface into the die cavity in response to the random movement of the ultrasonically actuated die. When the die was deactuated and disengaged from the contact surface, the precious metal which had been scrubbed from the contact surface into the die cavity defined a precious metal projection extending generally about the centerline axis of the electrical contact to a preselected height beyond the contact surface. The configuration of the precious metal projection conformed to that of the die cavity, and the free end portion of the precious metal projection defined a chordal section of a sphere having a spherical radius in a range between 0.004 and 0.007 inches with a centerpoint on the centerline axis of the electrical contact, and the aforementioned preselected height of the precious metal projection beyond the contact surface was in a range between 0.0025 and 0.0040 inches.
The above discussed prior art electrical contact was utilized in a prior art electrical device, such as for instance a push button switch or a cold control or the like. During the manufacture of the prior art electrical devices, foreign particles, such as for instance dust or metallic particles were found to be present, and it was believed that such foreign particles may have had a deleterious affect upon the making engagement of the prior art electrical contact with a cooperating stationary contact upon the energization of the electrical device. To counteract the presence of the foreign particles, a stream of ionized air was injected into the electrical device and passed over both the prior art electrical contact and the cooperating stationary contact. The effect of the ionized air stream was to displace the foreign particles of a size in excess of about 2 mils from the prior art electrical contact and the cooperating stationary contact; however, it was found that foreign particles of a size greater than about 1 mil and less than about 2 mils remained in place in engagement with both the prior art electrical contact and the cooperating stationary contact.
When the prior art electrical contact was moved into making engagement with the cooperating stationary contact upon the energization of the electrical device, the precious metal projection extending beyond the contact surface of the prior art electrical contact was abutted in circuit making engagement with the contact surface on the cooperating stationary contact. Thus, current was flowed through the precious metal projection between the prior art electrical contact and the cooperating stationary contacts and the circuit making engagement of the precious metal projection with the contact surface of the cooperating stationary contact effected a predetermined spacing apart of the respective contact surfaces on the prior art electrical contact and the cooperating stationary contact. Assuming that the electrical device was energized at 110 volts when the prior art electrical contact and the cooperating stationary contact were in circuit making engagement, as discussed above, the preselected height of the precious metal projection (i.e. between 0.0025 inches and 0.0040 inches) extending beyond the contact surface of the prior art electrical contact was great enough to accommodate the presence of the foreign particles sized greater than about 1 mil and less than about 2 mils which remained on the respective contact surfaces of the prior art electrical contact and the cooperating stationary contact subsequent to the above discussed introduction of the ionized .air stream into the electrical device.
When the prior art electrical contact and the cooperating stationary contact were disposed in circuit making engagement in the manner discussed hereinabove, the accommodation of the foreign particles sized greater than about 1 mil and less than about 2 mils between the respective contact surfaces of the prior art electrical contact and the cooperating stationary contact was particularly important within a designated "sphere of influence" between such contact surfaces. This designated "sphere of influence" extending between the contact surfaces of the prior art electrical contact and the cooperating stationary contact was defined within a generally circular area on the contact surface of the prior art electrical contact about the centerline axis thereof where foreign particles sized in excess of about 2 mils might have lodged between the respective contact surfaces of the prior art electrical contact and the cooperating stationary contact to prevent the circuit making engagement therebetween. The "sphere of influence" is a function of the curvatures or radii of the respective contact surfaces on the prior art electrical contact and the cooperating stationary contact and also the spherical radius of the chordal section of the sphere defined on the free end of the precious metal projection on the prior art electrical contact.
Even though the prior art electrical contact was fabricated by a method utilizing an ultrasonically actuated die in the manner discussed hereinabove, one of the disadvantageous or undesirable features of such fabrication method is believed to be that the cycle time of the ultrasonically actuated die to form one of the prior art electrical contacts was too slow and therefore too expensive from the view of manufacturing or fabricating time. Another disadvantageous or undesirable feature of the above discussed fabrication method is believed to be that the ultrasonic equipment necessary to actuate the die was not only too expensive as an initial or capital investment but also was too expensive to operate from the viewpoint of equipment shut down for necessary maintenance and repairs. Further, another disadvantageous or undesirable feature of the past fabrication method is believed to be that wear on the ultrasonically actuated dies was excessive necessitating frequent replacement thereof.